1. Field of the Disclosure
The present application relate to an organic t-emitting display device.
2. Description of the Related Art
Flat type devices for displaying information are being widely developed. The display devices include liquid crystal display devices, organic light-emitting display devices, electrophoresis display devices, field emission display devices, and plasma display devices.
Among these display devices, organic light-emitting display devices have the features of lower power consumption, wider viewing angle, lighter weight and higher brightness compared to liquid crystal display devices. As such, the organic light-emitting display device is considered to be next generation display devices.
Thin film transistors used in the organic light-emitting display device can be driven in high speed. To this end, the thin film transistors increase carrier mobility using a semiconductor layer which is formed from polysilicon. Polysilicon can be derived from amorphous silicon through a crystallizing process.
A laser scanning mode is widely used in the crystallizing process. During such a crystallizing process, the power of a laser beam may be unstable. As such, the thin film transistors formed along the scanned line, which is scanned by the laser beam, can have different threshold voltages from each other due to different mobilities in each thin film transistor. This can cause image quality to be non-uniform between pixel regions.
To address this matter, a technology detecting the threshold voltages of pixel regions and compensating for the threshold voltages of thin film transistors had been proposed.
A threshold voltage of the pixel region(s) is compensated with a compensation data that is generated based on the detected threshold voltage, such that a driving current is irrespective of the threshold voltage of the pixel region.
The driving current in which the threshold voltage is compensated is represented as the following.I=C(VDD−Vdata)2,
Wherein C is constant, VDD is a power supply voltage, and Vdata is a data voltage.
The method of the related art detects the threshold voltages of the thin film transistors during a fixed sensing interval, as shown in FIG. 6.
However, the above-mentioned crystallizing process using the laser beam forces the thin film transistors to have different mobilities. As such, when the sensing interval is fixed, the detected threshold voltage can be different due to variation of the mobility.
More specifically, if high mobility maintained during the sensing interval, the threshold voltage can be precisely detected. On the contrary, when low mobility is maintained during the sensing interval, a voltage higher than the real threshold voltage of the thin film transistor can be detected.
In other words, in the related art method using the fixed sensing interval, it is difficult to detect accurate threshold voltages. As such, the threshold voltages cannot be compensated for accurately. In accordance therewith, the non-uniformity of picture quality cannot be removed.
In addition, a mura phenomenon such as a line mura can be caused by different mobilities of the scanned lines. The line mura is generated when brightness between pixels on lines, for example gate lines in the display device are different from each other.
The sensing interval can be adjusted to be short, as shown in FIG. 7. In this case, variation of mobility can be reflected in the detected threshold voltage, but the mura phenomenon can be easily recognized in low gray scale levels.
On the contrary, the sensing interval can be adjusted to be long. In this case, non-uniformity of brightness caused by different threshold voltages can be removed, but it is not easy to eliminate the line mura which is caused by the variation of mobility in high gray scale levels.
Furthermore, as mobility in the sensing interval becomes lower, a voltage higher than an original data voltage is applied to a pixel region. Due to this, brightness defects can be caused.